Among various Silicon on Insulation (SOI) approaches SIMOX (separation by oxygen implantation) seems to be the most promising as an alternative for silicon on sapphire (SOS) in CMOS structures. During the SIMOX process, oxygen at the dose of about 1.0-2.0.times.10.sup.18 cm.sup.2 is implanted into a silicon wafer with energy of about 150-200 keV, within a temperature range of about 450.degree.-650.degree. C. To remove the implantation damage and to form a buried oxide layer, the SIMOX wafers are subsequently annealed at a temperature in the range from 1150.degree. to 1400.degree. C. A typical SIMOX structure is shown in FIG. 1 wherein a wafer 10 includes an oxygen implanted layer 12 and a regrown SIMOX film 14. A thin surface layer (.congruent. 10-20 nm) of the SIMOX wafers serves as a seed during the solid state regrowth process. The degree of crystalline perfection of this layer will influence the crystallographic perfection of the regrown SIMOX film 14.
It is well known that high density crystallographic defects of the SIMOX material and the presents of contaminants such as heavy metals and carbon adversely affect the ultimate performance of devices formed in the SIMOX material. Heavy metal and carbon contaminants which are commonly found in the SIMOX material originate from impurities which are sputtered from internal parts of the ion implantor itself. These contaminants appear in different form such as nuclei dispersed within the SIMOX material. Oxygen precipitates collect around these nuclei thereby forming crystallographic defects in the SIMOX material during high temperature annealing. It would be desirable to have a method of reducing the number of crystallographic defects by removing oxygen precipitates and by removing these contaminants from the SIMOX material prior to device fabrication.